Reactor-produced impact copolymers (“ICP”), in situ blends of propylene homopolymer and propylene/ethylene copolymer (“EP”), are widely available and used in such applications as automotive components and domestic appliances. In making such ICP's, a staged process is typically used whereby the propylene homopolymer is generated in at least one reactor, then that homopolymer is transferred to another stage or reactor to produce the EP, usually relying upon the same catalyst that is used to make the homopolymer. Typically, hydrogen is used in the homopolymer stage/reactor to control its melt flow rate (or molecular weight). When the propylene homopolymer is transferred to the propylene/ethylene stage/reactor the residual hydrogen will go along with it. That hydrogen then acts as a chain termination agent in the copolymerization reactor that generates propylene/ethylene copolymer, typically increasing its melt flow rate (lowering the molecular weight) of the EP. This may be undesirable because there is often a need to have a low melt flow rate (high molecular weight) copolymer component in the ICP. Thus, what is needed is a method of removing, preferably in a controlled manner, the hydrogen prior to entering, and/or within the copolymer stage/reactor. Mechanical means for removing the hydrogen prior to entering the copolymer stage/reactor are available such as a low pressure separation system, but this can be costly to build and operate. The inventors have overcome these and other problems.
Related publications include U.S. Pat. Nos. 9,045,569; 7,897,705; 4,980,421; 4,851,488; US 2013/0289277A1, and JP 08151408.